Interposers with electrically conductive features having different porosities

ABSTRACT

Interposer circuitry ( 130 ) is formed on a possibly sacrificial substrate ( 210 ) from a porous core ( 130 ′) covered by a conductive coating ( 130 ″) which increases electrical conductance. The core is printed from nanoparticle ink. Then a support ( 120 S) is formed, e.g. by molding, to mechanically stabilize the circuitry. A magnetic field can be used to stabilize the circuitry while the circuitry or the support are being formed. Other features are also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/380,172, filed on Dec. 15, 2016, incorporated herein byreference, which is a division of U.S. patent application Ser. No.14/602,984, filed on Jan. 22, 2015, incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention is directed to integrated circuits, and moreparticularly to interconnection of integrated circuits and othercomponents.

An integrated circuit (IC) is a small device with tiny contact pads thatmust be connected to other circuitry to form a complete system. ICs andother circuits are often interconnected through intermediate substratessuch as printed circuit boards (PCBs) or interposers. An IC's contactpads can be connected to the substrate's contact pads by discrete wires.However, to reduce the size of the assembly and shorten the electricalpaths, the discrete wires can be eliminated, as illustrated in FIG. 1.

FIG. 1 shows two ICs 110.1, 110.2 connected to each other and possiblyto other circuits through an interposer 120 and a PCB 124. In thisexample, each IC 110 (i.e. 110.1 and 110.2) is a “die” (also called“chip”), i.e. it is initially manufactured in a semiconductor wafer (notshown) together with other ICs, and the wafer is then cut up to separatethe ICs. The interposer includes a support 120S with conductive vias 130passing through the support. The interposer also includes aredistribution layer (RDL) 140 with conductive lines 140L insulated fromeach other by dielectric 140D. (The conductive lines may be arranged asone or more conductive layers; if there is only one conductive layer,the conductive lines can be horizontal, without vertical portions.) Thedies' contact pads 110C are attached to contact pads 120C.T provided atthe top of RDL 140.T. The connections are shown at 144, and can besolder, adhesive, diffusion bonding, or some other type. Discrete wirescan also be used. The RDL's conductive lines 140L interconnect thecontact pads 120C.T and the vias 130. The vias terminate at the bottomat contact pads 120C.B. Contact pads 120C.B are attached to the PCB'scontact pads 124C with other connections 144, e.g. solder or adhesive ordiffusion bonding. The PCB may include other contact pads connected toother circuits (ICs, interposers, or other components, not shown). ThePCB's conductive lines 124L interconnect the PCB's contact pads 124C asneeded.

PCB 124 and interposer 120 absorb and dissipate some of the heatgenerated by the die and thus reduce thermal stresses (mechanicalstresses resulting from thermal expansion). Also, if the interposer'scoefficient of thermal expansion (CTE) is intermediate between the PCBand the die, then the interposer may alleviate some of the stressesarising from the CTE mismatch between the die and the PCB. Further, thePCB manufacturing technologies may not allow the PCB contact pads 124Cto be as densely packed as the die's contact pads 110C, and in this casethe interposer 120 serves to “redistribute” the contact pads, i.e.provide the interconnection despite the positional mismatch between thedie's and PCB's contact pads.

The vias 130 can be formed by depositing metal into through-holes madein support 120S. However, it is often preferred that the through-holesbe narrow (in order to reduce the lateral area of the structure), andmetal deposition into narrow holes is complicated, resulting possibly inmetal discontinuities and voids which impair electrical conductivity andreliability. To address this problem, the fabrication process can bereversed: vias 130 can be initially formed as free-standing posts on asacrificial substrate 210 (FIG. 2A), and these posts can then beinserted into through-holes 148 in a separate support 120S (FIGS. 2A,2B). Substrate 210 can then be removed (FIG. 2C). See U.S. Pat. No.7,793,414 issued Sep. 14, 2010 to Haba et al. Posts 130 can be formed bydeposition and etch or by a selective deposition process. Selectivedeposition processes include electroplating, chemical vapor deposition(CVD), evaporation, sputtering, and printing.

It is desirable to provide improved processes and materials for forminginterconnections.

SUMMARY

This section summarizes some features of the invention. Other featuresmay be described in the subsequent sections. The invention is defined bythe appended claims, which are incorporated into this section byreference.

In some embodiments of the present invention, the vias 130 aremanufactured as free-standing posts similarly to FIG. 2A, possibly byusing novel techniques described below. Also, vias 130 can be replacedby other types of free-standing circuitry including, for example,conductive lines with vertical, horizontal, and inclined segmentsextending in any desired direction. Such circuitry may facilitatecontact-pad redistribution, possibly eliminating or simplifying the RDL140. Also, the circuitry may include coils and other shapes to provideinductors, capacitors, and possibly other circuit elements.

In some embodiments, such circuitry is made by printing of nanoparticleinks. A nanoparticle ink includes sub-micron-size conductive particles(e.g. copper, silver, or some other metal) dispersed in a liquid orsemisolid carrier (“solvent”). Nanoparticle ink can be deposited onto asubstrate (such as 210 in FIG. 2A) from a nozzle (or multiple nozzles,not shown) drop by drop or in a continuous flow. The ink can be forcedout of the nozzle by mechanical pressure (e.g. by air pressure, orpiezoelectrically, or by thermal pulses); or electrostatically (inelectrohydrodynamic printing). See e.g. U.S. pre-grant patentpublications 2011/0187798 A1 (Rogers et al.), 2013/0059402 (Mar. 7,2013; Jakob et al.), and 2014/0322451 (Oct. 30, 2014; Barton et al.);PCT publications WO 2009/011709 A1 and WO 2010028712 A1; U.S. Pat. No.7,922,939 B2 (Apr. 12, 2011; Lewis et al.); Ahn et al., “Planar andThree-Dimensional Printing of Conductive Inks”, J. Vis. Exp. (58),e3189, doi:10.3791/3189 (2011); U.S. Pat. No. 7,141,617 (Gratson et al.,Nov. 28, 2006); UK patent application no. 2 481 918 (12 Apr. 2006); andU.S. Pat. No. 7,790,061 (Sep. 7, 2010, Gratson et al.); all incorporatedherein by reference. Nanoparticle ink printing was also disclosed at anoral presentation by Heejoo Lee and Jang-Ung Park, “High-ResolutionPrinting of Three-Dimensional Structures by Electrohydrodynamic InkjetPrinting Using Multiple Functional Inks”, presented at 2014 MaterialsResearch Society Spring Meeting, San Francisco, Apr. 23, 2014.

When deposited on a substrate (such as 210), the conductivenanoparticles are held together (by van der Waals or other forces) toprovide a wire or other feature, and the solvent partially or completelyevaporates. Further, the nanoparticles can be sintered together, e.g. byheat. In some embodiments, the sintering temperature is quite low, wellbelow the melting temperature for the corresponding bulk materials, dueto the nanoparticles' high surface energy. For example, coppernanoparticles can be sintered at 200 to 300° C. or even below 200° C.This printing process can provide thin, strong, conductive wires, havingdown to sub-micron diameter and a high aspect ratio (the aspect ratio isthe ratio of the wire length to the wire diameter). The wires do nothave to be vertical but can be inclined at any angle, and can forminductor coils or other structures as needed.

After printing the wires, support 120S can be formed as a dielectriclayer encapsulating the wires. The dielectric can be formed for examplefrom a flowable (liquid or semisolid) material such as epoxy or glass orany suitable molding compound, or by chemical vapor deposition (CVD) orphysical vapor deposition (CVD). See U.S. pre-grant patent publicationUS 2014/0036454 A1 (Caskey et al., Feb. 6, 2014) entitled “BVAInterposer”, sharing common inventors and assignee with the presentapplication.

The inventors observed that even after sintering, the wires made fromnanoparticle inks can be highly porous, and hence may have relativelyhigh electrical resistance especially if the wires are thin (thin wiresare desirable for high packing density). In some embodiments, theporosity can be as high as 40% or higher (especially before sintering).The wires' conductivity can be quite low even after sintering due inpart to the porosity and in part to the resistive junctures between theadjacent particles. Therefore, in some embodiments, before thedielectric deposition, the wires are coated with a conductive coating(e.g. metal) to increase electrical conductivity. In some embodiments,the coating material is less porous, and/or has a higher electricalconductivity, than the material of the printed wires.

In some embodiments, an electrically insulating coating is formed overthe conductive coating to insulate the wires from support 120S. In thiscase, support 120S can be made of a non-electrically insulatingmaterial, possibly conductor or semiconductor. An insulating materialcan also be used. Thus, a greater choice of materials becomes availablefor support 120S, as needed for CTE matching, rigidity, or otherproperties.

Some embodiments do not use nanoparticle inks to print coils or othercircuit elements.

Another problem addressed by some embodiments of the present inventionrelates to maintaining the wires' shape during fabrication of support120S: if the wires bend, it may be impossible to connect them to denseoverlying features (such as die's contact pads 110C or RDL lines 140L).Therefore, in some embodiments, the wire shape is maintained by anexternal magnetic field. The wires' printed core or the coating mayinclude magnetic materials (ferromagnetic materials such as nickel,cobalt or iron, or ferrimagnetic materials such as ferrites or magneticgarnets), to enable magnetic control of the wire shapes. The magneticfield can be used with any free-standing wires or other circuitelements, not necessarily with wires made from nanoparticle inks, andeven with wires made by techniques other than printing.

The invention is not limited to the features and advantages describedabove except as defined by the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross section of an integrated circuit assemblywith an interposer according to prior art.

FIGS. 2A, 2B, 2C are vertical cross sections of structures withinterposers in the process of fabrication according to prior art.

FIG. 3A.1 is a vertical cross section of a structure with an interposerin the process of fabrication according to some embodiments of thepresent invention.

FIG. 3A.2 is a top view of a structure shown in FIG. 3A.1 according tosome embodiments of the present invention.

FIGS. 3B.1, 3B.2, 3C.1, 3C.2, 3D, 4 are vertical cross sections ofstructures with interposers in the process of fabrication according tosome embodiments of the present invention.

FIGS. 5A, 5B are flowcharts of fabrication processes according to someembodiments of the present invention.

FIGS. 6A, 6B, 6C, 7, 8A, 8B, 9, 10, 11, 12 are vertical cross sectionsof structures with interposers in the process of fabrication accordingto some embodiments of the present invention.

DESCRIPTION OF SOME EMBODIMENTS

The embodiments described in this section illustrate but do not limitthe invention. The invention is defined by the appended claims.

Below, the terms “conductivity”, “conductive”, “conductor”, etc. referto electrical conductivity unless stated otherwise. Similarly,“resistivity” relates to electrical resistivity, and “insulation” refersto electrical insulation, unless stated otherwise. “Dielectric” denotesany electrically insulating material, not necessarily with a highdielectric constant.

FIGS. 3A.1 (vertical cross section), 3A.2 (top view) illustrate printingof wire cores 130′ from nanoparticle ink 304 onto substrate 210 in someembodiments of the present invention. Cores 130′ are the core parts ofwires 130. The printing can use conventional technology described inreferences cited above, or other technology. In the embodiment shown,ink 304 is dispensed from a nozzle 310 by suitable forces, e.g.electrostatic or mechanical pressure (the mechanical pressure can begenerated by heat, gas pressure, piezoelectrically, or possibly in otherways). Ink 304 includes a suspension of conductive nanoparticles (“NP”)304P in a solvent 304S as shown in insert A. Particles 304P areschematically shown as circles (spheres), but they may have arbitrarythree-dimensional, possibly irregular shapes. Particles 304P are ofsub-micron sizes, sufficiently small to sinter at a desired lowtemperature (e.g. 300° C. or less). For example, in some coppernanoparticle embodiments, the copper particle size is below 0.5 microns,and most particles have a size below 108 nm; see e.g. Sunho Jeong etal., “Air-stable, surface-free Cu for highly conductive Cu ink and theirapplication to printed transistors”, J. Mater. Chem. C, 2013, 1,2704-2710, incorporated herein by reference, describing an ink with acopper particle sizes having a bimodal distribution with 42 nm and 108nm peaks. Particles 304P can be any suitable electrically conductivematerial, e.g. metal or metal alloy, and the metal can be copper,silver, nickel, cobalt, iron, tin, solder, or some other type. Particles304P can also be non-metallic conductors, e.g. carbon (such as graphiteor carbon black (such as acetylene black)), conductive ceramics (e.g.indium tin oxide or titanium nitride), conductive polymers (e.g.polypyrrole).

The solvent 304S can be any solvent described in the references citedabove. Other nanoparticle ink materials, known or to be invented, mayalso be suitable for the interposer fabrication processes describedbelow.

Substrate 210 can be any material consistent with subsequent processingand operation. For example, in some embodiments, substrate 210 will beremoved during fabrication, and the substrate material can be chosen tofacilitate easy removal. If fabrication involves high temperatures, thenthe substrate material can be chosen to have a CTE identical or similarto the CTE of other components (e.g. 304P, 120S, and others). Thesubstrate material should enable adequate adhesion of cores 130′ to thesubstrate. Substrate 210 can be conductive, dielectric, orsemiconductor. Exemplary conductive materials are the same as givenabove for particles 304P. Exemplary semiconductors are monocrystalline,polycrystalline, or amorphous silicon. Exemplary dielectrics are silicondioxide, silicon nitride, polyimide, epoxy. Both organic and inorganicmaterials can be used; composite materials are possible. Substrate 210can be rigid, semi-rigid, or flexible as desired. Rigid materials aresometimes preferred as they can be precisely positioned and can beeasily handled by robots; on the other hand, flexible materials arepreferred for reel-to-reel processing.

Substrate 210 can be a laminate of multiple layers of the same ordifferent materials. A part (possibly all) of the top layer can beelectrically conductive to enable subsequent electroplating ofconductive coating on cores 130′ as discussed below.

Nozzle 310 moves from one wire location to the next, or substrate 210 ismoved under the nozzle, or both are moved as needed. The nozzle and thesubstrate can also move vertically relative to each other (e.g. thenozzle moves while the substrate is stationary, or the substrate moveswhen the nozzle is stationary, or both move). The nozzle and/orsubstrate movement can be effected by hand or, more typically,automatically (possibly controlled by a computer pre-programmed with thedesired locations and heights of cores 130′, with parameters that definethe ink dispensing, and possibly other operational parameters). The inkcan be dispensed drop-by-drop or continuously (continuous dispensing canbe interrupted if needed while moving the nozzle relative to thesubstrate).

In FIG. 3A.2, the cores 130′ form an array, but this is a non-limitingexample as the wires can be at any locations. The cores are showncircular in top view, but they may be oval or have other shapes. A coremay have a varying horizontal cross section, e.g. a core may be wider atthe bottom than at the top or vice versa. For example, the bottomportion of a core may be formed by larger ink drops than the topportion, or by two laterally adjacent ink drops versus a single drop ateach horizontal level for the top. Different cores may have differentshapes and dimensions in the same interposer. Also, while the cores areshown as vertical, they can be of any shape as discussed below.

In some embodiments, each core's diameter (maximum dimension in topview) is 50 nm to 50 μm; the pitch (the minimum core/space distance, orthe minimum distance between the centers of adjacent cores) is 100 nm to100 μm; the core's height is up to 2 mm; the aspect ratio (height todiameter) is 3:1 to 50:1. The aspect ratio is limited by the need tokeep the wires rigidly positioned in later processing, but thisrequirement can be relaxed (and hence the aspect ratio can be increased)if magnetic fields are applied as described below. The effective aspectratio can be further increased by stacking multiple interposers on topof one another as described below in connection with FIG. 10.

The pitch can also be limited by the nozzle 310 diameter if the nozzle'sbottom is at a lower height than the adjacent already-printed cores 130′(as shown in FIG. 3A.1). However, if the nozzle is higher than the coresduring printing, then the nozzle diameter may be non-limiting withrespect to the pitch.

In some embodiments, multiple nozzles are used in parallel to printrespective different wires. For example, one wire array can be printedby one nozzle while another wire array can be simultaneously printed byanother nozzle. The nozzles can be spaced from each other by a greaterdistance than adjacent wires.

The structure is processed (e.g. heated) to sinter the nanoparticles304P in each core 130′. Conventional sintering processes can be used. Insome embodiments, the solvent completely or entirely evaporates beforeand/or during sintering.

A conductive coating 130″ is formed on cores 130′ as shown in FIG. 3B.1or 3B.2. Both figures show vertical cross sections. In FIG. 3B.1, thecoating 130″ is formed on cores 130′ only. In FIG. 3B.2, coating 130″ isalso formed between the cores. Coating 130″ has a lower porosity thancores 310′, possibly zero porosity. Coating 130″ is substantiallyconformal: it does not bridge the adjacent cores 130″ to allow the coresto be electrically insulated from each other if needed.

In some embodiments, coating 130″ is a higher electrical conductivitymaterial than cores 130′ due to the chemical composition and/or porosityand/or other properties of these materials. For example, coating 130″can be copper, iron, nickel, cobalt, silver, palladium, or some othermetal, or their alloys, deposited to a thickness of 100 nm or some otherthickness as needed to obtain the desired low resistance of wires 130 (awire 130 is a combination of a core 130′ and its coating 130″). Coating130″ may include a number of layers, possibly differing from each otherin chemical composition and/or porosity and/or other properties. Forexample, some of the layers may serve as barrier layers to preventdiffusion between a material in wires 130 and a subsequently depositedsupport material 120S.

Possible increase of electrical conductivity of wires 130 can beillustrated by the following examples. Suppose that right after printing(before sintering), cores 130′ have porosity of 30% or more. Afterlow-temperature sintering, the porosity may decrease to a value of 20 to30%. (High temperature sintering, e.g. 700° C. or more for copper, canreduce the porosity even further, e.g. to about 5%). Plated coating 130″may have porosity of 10% or less, possibly less than 5%. Assuming thepost-sintering core porosity of 20% and coating porosity of 10%, thecoating porosity is 50% lower than the post-sintering core porosity.Assuming the post-sintering core porosity of 30% and coating porosity of5%, the coating porosity is (30−5)/30=83% lower than the post-sinteringcore porosity. Other values are possible in this regard. The reducedporosity increases the electrical conductance in addition to conductancegains due to sintering.

In some embodiments, the sintering temperature for core 130′ can be 70%or less of the sintering temperature for the bulk material of thenanoparticles (in absolute temperature in Kelvin (K)), and possibly 50%or less of the melting temperature if the material has a meltingtemperature. For example, for copper nanoparticles the sinteringtemperature can be 300° C. (575° K) or less at atmospheric pressure,while the bulk melting temperature is 1085° C. (1358° K) and theconventional sintering temperature is above 650° C. (i.e. above 923° K).

In some low-temperature sintering embodiments, coating 130″ increasesthe conductance of a wire 130 by 5% or more, possibly 10% or 20% ormore. These numbers are exemplary and do not limit the invention. Forexample, a thicker coating may provide higher conductance gains.

In some embodiments, one or more layers of coating 130″ are formed byelectroless plating. If substrate 210 has a conductive top surface (e.g.if the substrate is conductive or has a conductive top layer), coating130″ can be formed by electroplating; the plating voltage can besupplied to the cores 130′ from a power source (not shown) connected tothe edge or bottom of substrate 210. In either case, depending on thesubstrate material, coating 130″ may or may not form on substrate 210between the cores, as shown in FIGS. 3B.2 and 3B.1 respectively. Coating130″ can also be formed by physical vapor deposition (e.g. sputtering),chemical vapor deposition (CVD), or possibly other techniques. In someembodiments, the coating 130″ includes multiple layers; one layer ismade by sputtering or CVD, and a subsequent layer or layers byelectroplating; the sputtered or CVD-deposited layer delivers theplating voltage and current to cores 130″ even if the substrate 210 isdielectric.

In some embodiments, the coating 130″ covers only the top segments ofthe cores. In another example, coating 130″ can be formed by dipping thecores into a liquid or semisolid material to coat the cores, and thencuring the material, if the cured material is conductive. Exemplarymaterials of this kind are solders, indium, nickel, poly(pyrrole)s, andpoly(acetylene)s. The cores 130′ should preferably be wettable by theliquid or semisolid material. Substrate 210 may or may not be wettable.In some embodiments, the cores are only partially dipped into the liquidor semisolid material, and the coating 130″ covers only the top sectionsof the cores, above the desired level.

Coating 130″ may at least partly fill the open pores of cores 130′.

Advantageously, the porous surface of cores 130′ improves the platingspeed and adhesion of coating 130″ and reduces stress or strain due tothe CTE mismatch between the core and the support materials.

As shown in FIG. 3C.1 (for the case of FIG. 3B.1) and FIG. 3C.2 (for thecase of FIG. 3B.2), dielectric 120S is formed to encapsulate the wires130 and cover the substrate 210. Dielectric 120S fills the area abovethe substrate 210 up to a certain level, possibly to the tops of wires130 (as shown) or to a lower level, but the tops are exposed. In someembodiments, the dielectric 120S is an encapsulant (a molding compound),i.e. a flowable material (possibly gel) that can be flowed onto thesubstrate (e.g. by molding, or without a mold) and then cured (by heat,UV light, or some other technique) to provide a solid dielectric layer.Such encapsulant materials include polymers and other materials based onpolyimides (e.g. type PI-2611 available from Dupont), or based onepoxies, silicone, polyurethane, poly-phenylene benzobisoxazole (PBO),or benzocyclobutene (BCB). Glass can be used (possiblylow-melting-temperature spin-on glass), and possibly other organic andinorganic materials. These materials may be augmented with fillers thatmay reduce the material cost and/or help achieve desired properties withrespect to resistivity, CTE, rigidity, hardness, thermal conductivity,and possibly other factors. For example, a CTE may be desirable thatmatches the CTE of wires 130 and/or die 110 and/or underfill orencapsulant (not shown) formed under and over the die, and/or othercomponents.

Alternatively, dielectric 120S can be formed by PVD, CVD, or electrolessor electrolytic plating, or possibly some other method or combination ofmethods. For example, silicon dioxide or silicon nitride can be used andcan be formed by CVD.

In some embodiments, the dielectric initially covers the wires 130 butthen is thinned (e.g. by etching or chemical and/or mechanicalpolishing, possibly blasting with abrasive particles) as needed toexpose the tops of wires 130. The dielectric may or may not have aplanar top surface.

In some embodiments, support 120S is formed as in FIGS. 2A-2B, i.e. as aseparate structure with a hole for each wire 130.

As shown in FIG. 3D, substrate 210 is removed. In the case of FIG. 3C.2,the coating 130″ is also removed between the wires so as to electricallyinsulate the wires from each other. Alternatively, portions of coating130″ may be left in place between the wires to interconnect some of thewires 130. These wires may be interconnected to form desired circuitry,or perhaps these wires are not part of any circuitry but are used toenhance heat dissipation and/or mechanical strength of the interposer,and these wires can be left interconnected by layer 130″ to furtherenhance heat dissipation and/or mechanical strength and/or otherproperties.

In some embodiments, the bottom surface of dielectric 120S is planarwhen the substrate is removed. Bottom portions of wires 130 may beremoved in this process so that the wires' bottoms are coplanar with thebottom surface of dielectric 120S. Alternatively, the wires' bottoms canbe recessed into, or protruding out of, the bottom surface of dielectric120S to facilitate subsequent alignment and connection with otherfeatures (such as PCB contacts 124C shown in FIG. 1).

Removal of substrate 210, and of layer 130″ between the wires in thecase of FIG. 3C.2, can be performed by chemical etching, mechanical orchemical mechanical polishing (including for example grinding ormilling), or any other technique or combination of techniques. In thecase of FIG. 3C.2, if some of layer 130″ interconnecting the wires is tobe left in place, then substrate 210 can be removed first, and thenlayer 130″ can be patterned as needed using photolithography forexample. In some embodiments, substrate 210 is removed by a blanketprocess (without a mask), and in some embodiments in the case of FIG.3C.2 the entire layer 130″ portion between the wires 130 is also removedwithout a mask.

Subsequent processing can be as in prior art or of some other type. Forexample, in FIG. 4, RDL 140.T is formed on top of support 120S, and RDL140.B is formed on the bottom. Contact pads 120C.T and contact pads120C.B are formed at the top and bottom of interposer 120 respectivelyat the ends of lines 140L of the respective RDLs. Each RDL 140 (140.Tand 140.B) includes conductive lines 140L that interconnect the wires130 and, respectively, the top contact pads 120C.T (for RDL 140.T) orthe bottom contact pads 120C.B (for RDL 140.B). Each RDL 140 may includedielectric 140D—e.g. organic dielectric, possibly a polymer (e.g.polyimide), or inorganic dielectric, e.g. silicon dioxide or siliconnitride—that electrically insulates the conductive lines 140L from eachother and, possibly, from wires 130, as needed.

Chips 110 (or multichip modules) have their contact pads 110C connectedto the top contact pads 120C.T. The connections are shown at 144, andcan be solder, adhesive, diffusion bonding, or some other type. Discretewires can also be used. The chips 110 can be underfilled andencapsulated by a molding compound if desired. PCB 124 has its contactpads 124C attached to contact pads 120C.B, with connections also shownat 144; these connections can be solder, adhesive, or diffusion bonding.PCB contacts 124C are interconnected by PCB interconnects 124L. Othercircuits and connection types can be used to connect various circuits tocontact pads 120C (i.e. 120C.T and 120C.B) as known in the art. Further,RDL 140.T or 140.B or both can be omitted; the contact pads can beprovided by wires 130.

FIG. 5A illustrates a flowchart of the process described above. At step510, cores 130′ are printed as described above in connection with FIGS.3A.1, 3A.2. At step 520, coating 130″ is formed (FIG. 3B.1, 3B.2). Atstep 530, support 120S is formed (FIGS. 3C.1, 3C.2). At step 540,substrate 210 is removed, possibly with portions of coating 130″ and/orcores 130′ (FIG. 3D). At step 550, the RDLs are formed (FIG. 4). At step560, die 110 and PCB 124 are added to the structure.

Many variations are possible. For example, removal of substrate 210(step 540) can be postponed as shown in FIG. 5B. Here the steps 510,520, 530 are performed in the same sequence as in FIG. 5A. Then RDL140.T is formed (step 550A), and the die 110 are attached on top (step560A). Substrate 210 remains in place for steps 550A and 560A,strengthening the structure. Substrate 210 is removed after the dieattachment (step 540), and possibly after the die are underfilled andencapsulated by a molding compound. Bottom RDL 140.B is formed next(step 550B), followed by the PCB attachment (step 560B). Otherfabrication sequences and variations are possible.

Also, after forming the support 120S, the exposed portions (the tops) ofwires 130 can be plated with additional conductive material, e.g. abarrier layer (not shown) to prevent diffusion of materials of wires 130into dielectric 140D or of the dielectric material into the wires.

In another variation, support 120S is possibly non-dielectric material,and can be a conductor or semiconductor (but can also be dielectric).Before fabrication of support 120S, the wires 130 are coated bydielectric 610 (FIG. 6A) which will separate and electrically insulatethe wires from subsequently formed support 120S (FIG. 6B). In someembodiments, dielectric layer 610 is shown as substantially conformal,but this is not necessary. Dielectric 610 is removed at the top of wires130 (e.g. by a chemical etch or mechanical polishing or bombardment byenergized particles (like in PVD) or CMP or some other process) to allowthe wires to be contacted by lines 140L or contact pads 110C. Dielectriccoating 610 can be a thin film deposited over the wires 130 and,possibly, between the wires 130. FIGS. 6A-6C show the structurepre-processed as in FIG. 3B.1, with coating 130″ being absent betweenthe wires, but the initial structure can be as in FIG. 3B.2. If support120S is dielectric, it can be formed using the materials and processesdescribed above. Alternatively, support 120S can be a non-dielectricmaterial, e.g. metal or (possibly heavily doped) silicon, made by vapordeposition or other techniques, and having good heat dissipationproperties. RDL dielectric 140D can be formed on top and bottom toinsulate the support 120S from lines 140L or other conductive features,and the dielectric can be patterned to expose the wires 130 and providephysical and electrical access to the wires.

The wires 130 do not have to be vertical but may be at any angle and maybe curved and intersecting (i.e. branching), possibly eliminating theneed for the RDLs, as shown in FIG. 7. The wires are shown as blacklines, without showing the cores 130′ as separate from the coating 130″,but the wires can have the same structure as in FIG. 3D or 6C;dielectric 610 is not shown but may be present. In FIG. 7, wire 130.1 isvertical as in FIG. 3D. Wire 130.2 is bent. Wires 130.3 and 130.4 mergeat the bottom. Wire network 130.5 includes intersecting wires. Wire130.6 is a coil; the planar vertical cross section of FIG. 7 includesonly isolated points on the left and right of the coil plus the top andbottom connecting segments; the coil is schematically shown in insert A.Any shapes and networks of wires can be present. For example, wires canbe inclined to come closer together at the top than at the bottom of theinterposer to accommodate the smaller pitch of the die contact pads 110Ccompared to PCB contact pads 124C. The wire thickness can vary withinthe network, e.g. the wires can be thinner at the top than at the bottomto further facilitate attachment to structures with different contactpad pitches at the top of the interposer compared to the bottom.

RDLs 140 can be formed on top and/or bottom of the interposer as in FIG.4. However, flexibility in wire arrangements allows the wires 130 toreplace one or more (possibly all) of RDL interconnect lines 140L, sothe RDLs can be omitted or simplified. But RDLs can be used if desired.For example, some embodiments use RDLs because in such embodiments theconductive lines 140L can be thinner and closer to each other than wires130.

In some embodiments, each continuous network of wires is coated by acoating such as 130″ in FIG. 3D. However, the coating may cover onlypart of the network (due for example to limitations of the coatingprocess—e.g. if the coating is formed by sputtering then part of thenetwork can be shielded from the coating). In some embodiments, coating130″ is omitted. In some embodiments, the printing ink isnon-nanoparticle ink, i.e. its conductive particles are larger than 1micron in diameter. Sintering can be performed at high temperatures,i.e. same temperatures as for the corresponding bulk materials.

In FIGS. 8A, 8B, before printing step 510, a die or multi-chip module(MCM) 710 was formed on substrate 210 (any number of die or MCMs can bepresent). Substrate 210 may be a sacrificial substrate as describedabove. Module 710 may have bottom contact pads 710C.B, and possibly topcontact pads 710C.T on top. Some of wires 130 (e.g. 130.1) can be formedon the top contact pads 710C.T at steps 510-520 (these wires can be NPor non-NP, coated or not with 130″ and/or 610, of any configurationdescribed above in connection with FIG. 7).

Substrate 210 is removed at step 540 (FIG. 8B). In the particularembodiment of FIG. 8B, an RDL 140.B is formed on the bottom (step 550).Module 710 has contact pads connected to the RDL's lines 140L. Otherprocessing can be as described above (e.g. die and/or PCB attachment,with or without an RDL at the top). FIG. 8B shows a bottom RDL 140.B andconnections 144 as in FIG. 4, but the RDL can be absent and othervariations are possible.

In FIG. 9, substrate 210 is a non-sacrificial, functional substrate,with circuitry (not shown except for the top contact pads 210C). Modules710 may or may not be present. In FIG. 9, a module 710 is present, andits bottom contact pads 710C.B are attached to contact pads 210C withconnections 144 (e.g. solder or other types described above). Wires 130are formed on contact pads 210C and 710C.T. Additional features can beas described above (e.g. top RDL and die). This structure can bemanufactured as described above, but step 540 is omitted. The functionalsubstrate 210 can be another interposer as discussed immediately below.

In FIG. 10, interposer 120 includes three constituent interposers 120.1,120.2, 120.3 (any number of constituent interposers can be present).Each constituent interposer 120.i (i=1, 2, 3) is as in FIG. 3D or 6C orsome other type. In some fabrication processes, interposer 120.1 isformed on a sacrificial substrate 210 (not shown) as in FIG. 3D. Thesacrificial substrate is then removed (or can be removed at a laterstage). Then interposer 120.2 is formed on interposer 120.1 (i.e.interposer 120.1 serves as functional substrate 210 of FIG. 9). Theninterposer 120.3 is formed on interposer 120.2 (interposers 120.1, 120.2serve as substrate 210 of FIG. 9). Alternatively, interposer 120.2 canbe formed first, then interposer 120.1, then interposer 120.3.Additional constituent interposers (not shown) can be formed on top orbottom. Of note, any structures described in this disclosure can beturned upside down or at any angle if needed in fabrication orsubsequent use.

In FIG. 10, each wire 130 of interposer 120.3 is formed on top of acorresponding wire of interposer 120.2, which in turn is formed on topof a corresponding wire of interposer 120.1, resulting in triple-height(and triple aspect ratio) wires. Before forming the wires 130 ofinterposer 120.2, the wires of interposer 120.1 are encapsulated bycorresponding support 120S and are therefore mechanically stable.Likewise, the wires of interposer 120.2 are encapsulated bycorresponding support 120S before formation of wires 130 of interposer120.3. The mechanical stability facilitates fabrication of high aspectratio wires.

RDLs 140 can be formed between the constituent interposers asillustrated in FIG. 11—an RDL is formed between interposers 120.1 and120.2. The RDL's lines 140L interconnect the bottoms of wires 130 ofinterposer 120.2 and the tops of wires 130 of interposer 120.1 in anydesired manner. For example, interposer 120.1 can be formed first withthe RDL, then interposer 120.2 can be formed on top; or interposer 120.2can be formed first with the RDL, then interposer 120.1 can be added atthe bottom.

Also, a constituent interposer 120.i may include a module like 710 inFIGS. 8A-9. Other variations described above for a non-stackedinterposer can be present in stacked interposers.

Different constituent interposers may have respective differentstructure in the same interposer 120. For example, in FIG. 11,interposer 120.2 includes an X-shaped network of wires 130.1, butinterposers 120.1 and 120.3 may have only vertical wires. Some but notall interposers may include a dielectric coating 610 (FIGS. 6A-6C) ontheir wire structures. Different materials can be used for differentconstituent interposers. The constituent interposers may differ inthickness, in the pitch between conductive features 130, and otherproperties.

To stabilize the wires 130 during fabrication of support 120S, magneticfields can be used as shown in FIG. 12. Here the interposer 120 is as inFIG. 3B.1, but other interposer structures described above can be used.The structure is shown during fabrication of support 120S, which hasbeen partially formed. Wires 130 include magnetic material present inthe wire cores 130′ and/or coating 130″, and/or there is magneticmaterial in coating 610 (FIG. 6B). In this embodiment, the wires arekept in vertical position by a vertical magnetic field B. The field isdirected upward, but can be directed downward. The field is created byan electric current through a coil (solenoid) 1210 wound around thewires. The field could be created in any other suitable way, e.g. bypermanent magnets above and below the interposer. The field is generatedsince before the start of deposition of support material 120S, and thefield can be maintained as long as needed, possibly through the end ofthe deposition.

The magnetic field can also be used for the fabrication process shown inFIGS. 2A-2B, or for other processes.

In some embodiments, the wires are designed to be sloped (non-vertical),and the field B is generated to keep the wires at the desired angle.Also, in some embodiments, different wires have different angles, butsome wires are thicker and stronger (more stable) than others, and thefield B is directed to stabilize the weaker wires even though the fieldmay be transverse (angled) relative to the stronger wires. Further, insome embodiments, the field B helps stabilize curved wires. For example,in case of coil 130.6 in FIG. 7, a vertical field B helps keep the coilin the upright position.

The field B may have different directions at different parts of theinterposer to point different wires 130 at different angles in the sameinterposer.

The magnetic field can stabilize the wires in other manufacturingprocesses, e.g. in forming the coating 130″ (FIGS. 3B.1 and 3B.2) ordielectric coating 610. Indeed, when the coating 130″ or 610 is beingformed, the wires 130 may undesirably bend out of shape, and this maynegatively affect the coating uniformity. For example, if the coating isformed by sputtering, then a bent wire may shield part of an adjacentwire or part of its own surface from the sputtered material. Themagnetic field helps keep the wires in a desired shape during themanufacturing process.

The magnetic field can be used in this way with wires 130 formed asdescribed above or other types of wires, e.g. from nanoparticle inks orby other methods, with or without coating 130″ and/or coating 610, e.g.bond wires as in the aforementioned Caskey et al. US 2014/0036454publication, or possibly of other kinds.

In some embodiments, the magnetic field is strong enough to change theangular orientation of at least part of a wire by at least 1°, or atleast 5°, or at least 10°.

Suitable magnetic materials for wires 130 (e.g. for cores 130′ andcoatings 130″ or for the bond wires) include ferromagnetic materialssuch as iron, cobalt, and nickel, and ferrimagnetic materials such asferrites and magnetic garnets. The content of these materials in a wirecan be less than 100%, e.g. can be in the range of 3 to 99% by weight.The field B may or may not be uniform.

A magnetic field can be used at other fabrication stages, e.g. duringthe deposition of coating 130″ (FIGS. 3B.1, 3B.2) or coating 610 (FIG.6A), to stabilize the wires 130 or cores 130′ if they contain magneticmaterials.

The invention is not limited to the embodiments discussed above. Someembodiments are defined by the following clauses.

Clause 1 defines a method for manufacturing a structure comprising aninterposer comprising:

a support; and

interconnection circuitry passing through the support to interconnectcircuits above and below the interposer (interconnection circuitry mayinclude wires 130, and may include RDL lines 140L; the interposer may ormay not include any RDLs; the interposer may or may not include a module710), the interconnection circuitry comprising one or more electricallyconductive features (e.g. 130);

the method comprising:

(1) forming at least part of the interconnection circuitry on asubstrate, said at least part of the interconnection circuitrycomprising a core portion (e.g. 130′, the core portion may includemultiple cores of multiple wires) and an electrically conductive layer(e.g. 130″) overlaying at least part of the core portion andsubstantially conforming to the core portion, wherein forming the atleast part of the interconnection circuitry comprises:

-   -   depositing ink onto the substrate, the ink comprising conductive        nanoparticles carried by a non-gaseous fluid carrier (i.e.        liquid or semi-solid carrier), the conductive nanoparticles        joining together to form the core portion, the core portion        comprising one or more elongated segments above the substrate        (e.g. each elongated segment may be part of a core 130′ above        the substrate, e.g. the middle of the core of a wire 130 or any        other portion of the core; different elongated segments may be        different parts of a core 130′ or parts of different cores        130′); and    -   forming the electrically conductive layer over at least said        part of the core portion to increase the electrical conductance        of at least one conductive feature, the electrically conductive        layer covering an entire longitudinal surface of each elongated        segment;

(2) forming the support that fills, at least up to a level above eachelongated segment, a region above the substrate around each elongatedsegment, the support not completely covering said at least part of theinterconnection circuitry to allow at least each elongated segment to beelectrically contacted from above the support.

Clause 2 defines the method of clause 1 further comprising, afterforming the support, removing at least part of the substrate to enableat least one elongated segment to be electrically contacted from belowthe support.

Clause 3 defines the method of clause 2 wherein removing said at leastpart of the substrate exposes the interconnection circuitry at a bottomof the support.

Clause 4 defines the method of clause 2 wherein removing said at leastpart of the substrate comprises removing the substrate.

Clause 5 defines the method of clause 1 wherein forming the supportcomprises dispensing and curing a non-gaseous fluid material (e.g.encapsulant) at least a portion of which forms the support when cured.

Clause 6 defines the method of clause 1 wherein the electricallyconductive layer increases conductance of at least one elongated segmentby at least 5%.

Clause 7 defines the method of clause 1 wherein the electricallyconductive layer has a lower porosity than the porosity of at least oneelongated segment immediately before forming the electrically conductivelayer. Of note, the core porosity may be reduced by the electricallyconductive layer getting into the core pores.

Clause 8 defines the method of clause 7 wherein the porosity of theelectrically conductive layer is lower than the porosity of said atleast one elongated segment immediately before forming the electricallyconductive layer by at least 50%.

Clause 9 defines the method of clause 1 further comprising, afterforming the electrically conductive layer but before forming thesupport, forming a dielectric layer over the electrically conductivelayer over each elongated segment.

Clause 10 defines the method of clause 9 wherein the support is notdielectric, and the dielectric layer electrically insulates eachelongated segment from the support.

Clause 11 defines the method of clause 1 wherein the support isdielectric.

Clause 12 defines the method of clause 1 wherein the elongated segmentcomprises a coil.

Clause 13 defines the method of clause 12 wherein the coil comprises atleast two full turns.

Clause 14 defines the method of clause 1 further comprising, afterforming the support, forming dielectric and conductive layers on thesupport to form circuitry above the support (e.g. to form the RDL), thecircuitry above the support being part of the interconnection circuitry.

Clause 15 defines the method of clause 1 wherein:

the core portion comprises a plurality of spaced apart electricallyconductive core features (e.g. cores 130′); and

the electrically conductive layer is formed by electroplating when thecore features are electrically connected to a source of electric powerthrough an electrically conductive region interconnecting the corefeatures (e.g. through substrate 210 or a layer sputtered over the cores130′).

Clause 16 defines the method of clause 15 wherein the electricallyconductive region comprises at least part of the substrate.

Clause 17 defines the method of clause 15 wherein the electricallyconductive region comprises a layer formed over the core features.

Clause 18 defines the method of clause 1 wherein at least part of theinterconnection circuitry formed before forming the support comprisesmagnetic material, and wherein the magnetic material is placed in amagnetic field during interposer manufacturing to stabilize at leastpart of the interconnection circuitry. For example, the wholeinterconnection circuitry can be made of a magnetic material. In anotherexample, the interconnection circuitry comprises magnetic particlesmixed with conductive nanoparticles or present in a coating such as 130″or 610. In another example, coating 130″ and/or 610 is made entirely ofa magnetic material, and/or an additional coating is provided madeentirely or partly of a magnetic material.

Clause 19 defines the method of clause 18 wherein the magnetic materialis in the magnetic field during forming at least part of the support.

Clause 20 defines a structure comprising an interposer comprising:

a support; and

interconnection circuitry passing through the support and operable tointerconnect circuits above and below the interposer, theinterconnection circuitry comprising:

one or more first contact pads at a top of the interposer (e.g. pads120C.T);

one or more second contact pads at a bottom of the interposer (e.g.120C.B); and

one or more electrically conductive features interconnecting the firstand second contact pads in a desired pattern;

wherein the one or more electrically conductive features comprise:

one or more porous elongated segments underlying a top surface of thesupport; and

for each elongated segment, an electrically conductive layer covering anentire longitudinal sidewall of the elongated segment and substantiallyconforming to the longitudinal sidewall of the elongated segment, theelectrically conductive layer having a lower porosity than the elongatedsegment.

Clause 21 defines the structure of clause 20 wherein the support is madeof a molding compound.

Clause 22 defines the structure of clause 20 wherein the electricallyconductive layer increases conductance of at least one elongated segmentby at least 5%.

Clause 23 defines the structure of clause 20 wherein each elongatedsegment comprises a porous matrix made of a first conductive material,and the electrically conductive layer is made of a second materialdifferent from the first material, and the porosity of the electricallyconductive layer is lower than the porosity of the porous matrix by atleast 50%.

Clause 24 defines the structure of clause 20 further comprising adielectric layer over the electrically conductive layer of eachelongated segment, the dielectric layer substantially conforming to thelongitudinal surface of each elongated segment.

Clause 25 defines the structure of clause 24 wherein the support is notdielectric, and the dielectric layer electrically insulates eachelongated segment from the support.

Clause 26 defines the structure of clause 20 wherein the support isdielectric.

Clause 27 defines the structure of clause 20 wherein the elongatedsegment comprises a coil.

Clause 28 defines the structure of clause 27 wherein the coil comprisesat least two full turns.

Clause 29 defines the structure of clause 20 comprising dielectric andconductive layers on the support that comprise circuitry above thesupport, the circuitry above the support being part of theinterconnection circuitry.

Clause 30 defines a manufacturing method comprising:

forming a structure comprising one or more conductive features on asubstrate, the one or more conductive features comprising ferromagneticor ferrimagnetic material;

placing the one or more conductive features in a magnetic field tostabilize a position of the one or more conductive features; and

applying a manufacturing process to the structure when the conductivefeatures being stabilized by the magnetic field.

Clause 31 defines the method of clause 30 wherein the manufacturingprocess comprises forming at least part of a support on the substrate,the support laterally surrounding each conductive feature andstabilizing the position of each conductive feature.

Clause 32 defines the method of clause 30 wherein the manufacturingprocess comprises forming at least part of a conformal layer over eachconductive feature.

Clause 33 defines the method of clause 30 wherein the magnetic fieldchanges an angular orientation of at least one conductive feature by anangle of at least 1°.

Clause 34 defines the method of clause 30 wherein the angle is at least5°.

The invention is not limited to the embodiments described above. Otherembodiments and variations are within the scope of the invention, asdefined by the appended claims.

What is claimed is:
 1. A structure comprising an interposer comprising:a support; and interconnection circuitry passing through the support andoperable to interconnect circuits above and below the interposer, theinterconnection circuitry comprising: one or more first contact pads ata top of the interposer; one or more second contact pads at a bottom ofthe interposer; and one or more electrically conductive featuresinterconnecting the first and second contact pads in a desired pattern;wherein the one or more electrically conductive features comprise: oneor more porous elongated segments underlying a top surface of thesupport; and for each elongated segment, an electrically conductivelayer covering an entire longitudinal sidewall of the elongated segmentand substantially conforming to the longitudinal sidewall of theelongated segment, the electrically conductive layer having a lowerporosity than the elongated segment.
 2. The structure of claim 1 furthercomprising a dielectric layer over the electrically conductive layer ofeach elongated segment, the dielectric layer substantially conforming tothe longitudinal surface of each elongated segment.
 3. The structure ofclaim 2 wherein the support is not dielectric, and the dielectric layerelectrically insulates each elongated segment from the support.
 4. Thestructure of claim 1 wherein at least one elongated segment comprises acoil.
 5. The structure of claim 4 wherein the coil comprises at leasttwo full turns.
 6. The structure of claim 1 comprising dielectric andconductive layers on the support that comprise circuitry above thesupport, the circuitry above the support being part of theinterconnection circuitry.
 7. The structure of claim 1 wherein at leastone elongated segment is curved.
 8. A structure comprising an interposercomprising: a support; and interconnection circuitry passing through thesupport and operable to interconnect circuits above and below theinterposer, the interconnection circuitry comprising: one or more firstcontact pads at a top of the interposer; one or more second contact padsat a bottom of the interposer; and one or more electrically conductivefeatures interconnecting the first and second contact pads in a desiredpattern; wherein the one or more electrically conductive featurescomprise: a plurality of porous elongated segments underlying a topsurface of the support, wherein at least one of the segments extends ina different direction than another one of the segments; and for eachelongated segment, an electrically conductive coating covering an entirelongitudinal sidewall of the elongated segment and extending along theelongated segment, the electrically conductive coating having a lowerporosity than the elongated segment.
 9. The structure of claim 8 whereinthe electrically conductive coating increases conductance of at leastone elongated segment by at least 5%.
 10. The structure of claim 8wherein each elongated segment comprises a porous matrix made of a firstconductive material, and the electrically conductive coating is made ofa second material different from the first material, and the porosity ofthe electrically conductive coating is lower than the porosity of theporous matrix by at least 50%.
 11. The structure of claim 8 furthercomprising a dielectric layer over the electrically conductive coatingof each elongated segment, the dielectric layer substantially conformingto the longitudinal surface of each elongated segment.
 12. The structureof claim 11 wherein the support is not dielectric, and the dielectriclayer electrically insulates each elongated segment from the support.13. The structure of claim 8 wherein the support is dielectric.
 14. Thestructure of claim 8 wherein at least one elongated segment comprises acoil.
 15. The structure of claim 14 wherein the coil comprises at leasttwo full turns.
 16. The structure of claim 8 comprising dielectric andconductive layers on the support that comprise circuitry above thesupport, the circuitry above the support being part of theinterconnection circuitry.
 17. A structure comprising an interposercomprising: a support; and interconnection circuitry passing through thesupport and operable to interconnect circuits above and below theinterposer, the interconnection circuitry comprising: one or more firstcontact pads at a top of the interposer; one or more second contact padsat a bottom of the interposer; and one or more electrically conductivefeatures interconnecting the first and second contact pads in a desiredpattern; wherein the one or more electrically conductive featurescomprise a plurality of electrically conductive wires each of whichpasses through the support, at least two of the wires intersecting witheach other, each wire comprising: one or more porous elongated segmentsunderlying a top surface of the support; and for each elongated segment,an electrically conductive layer covering an entire longitudinalsidewall of the elongated segment and having a lower porosity than theelongated segment.
 18. The structure of claim 17 wherein at least onewire is curved.
 19. The structure of claim 17 wherein the electricallyconductive layer increases conductance of at least one elongated segmentby at least 5%.
 20. The structure of claim 17 wherein each elongatedsegment comprises a porous matrix made of a first conductive material,and the electrically conductive layer is made of a second materialdifferent from the first material, and the porosity of the electricallyconductive layer is lower than the porosity of the porous matrix by atleast 50%.